Cathodic electrodeposition of a film composed of amine resin, crosslinker, pigment, grind resin and other resinous components onto an electrically conductive article is an important industrial process. It constitutes the usual manner in which automobile and truck bodies as well as appliance and other large metallic surface bodies are undercoated with paint. In addition to providing a painted surface, the resin systems employed protect the underlying metal surface from corrosion, impact damage and other detrimental exposure to environmental conditions.
In performing the electrodeposition, the conductive article forms one electrode and is immersed in a coating bath made from an aqueous dispersion of the film-forming resin and other components. An electrical current is passed between the article and the counter electrode in the electrodeposition bath. A charge on the article causes deposition of the resins and other components in the bath so as to produce the electrodeposited film. The deposited film is then baked or otherwise hardened to yield a coating of a substantially uniform thickness having protective characteristics.
Pigment and pigment grind resins constitute important components of the coating bath and are deposited as part of the coating. Therefore, design characteristics are important for the grind resin as well as the other components of the coating. Such patents as U.S. Pat. Nos. 3,936,405 and 4,035,275, the disclosures of which are incorporated herein by reference, as well as others describing beneficial characteristics for such grind resins.
Pigment grind resins are included in the coating in order to increase the dispersion stability of the inorganic and/or organic pigments which may be present in the coating bath.
Most commercial cathodic electrocoat systems presently used employ a quarternary ammonium functional pigment dispersion/stabilization polymer. For example, U.S. Pat. No. 3,936,405 (Sturni et al.) describes the use of quaternary onium salt group-containing epoxy resins which are prepared by reacting amine salts, phosphine-acid mixtures or sulfide-acid mixtures with a 1,2-epoxy group containing material wherein a ratio of at least 0.4 equivalents of quaternary onium groups are said to be produced for equivalent of epoxy group initially present.
Although quaternary ammonium polymers have been found to be very effective, their preparation can be difficult and inconsistent.
It is therefore an object of the present invention to provide a pigment grind resin which maximizes the dispersing efficiency and dispersion stability of inorganic and organic pigments in an aqueous system.
It is another object of the present invention to provide a pigment grind resin which maximizes dispersing efficiency and dispersion stability which is not a quaternary ammonium polymer.
It is another object of the present invention to provide a pigment grind resin which is compatible with a wide range of electrodepositable resin systems
It is yet another object of the present invention to provide a pigment grind resin which is pH dependent and whose pH can be adapted to the pH of the principle amine resin.